1. Field of the Invention
The present invention relates to a thin-film magnetic head having at least an induction-type magnetic transducer and a method of manufacturing such a thin-film magnetic head, and to a thin-film coil element incorporated in a thin-film magnetic head and so on and a method of manufacturing such a thin-film coil element.
2. Description of the Related Art
Performance improvements in thin-film magnetic heads have been sought as surface recording density of hard disk drives has increased. Such thin-film magnetic heads include composite thin-film magnetic heads that have been widely used. A composite head is made of a layered structure including a recording head having an induction-type magnetic transducer for writing and a reproducing head having a magnetoresistive (MR) element for reading.
It is required to increase the track density on a magnetic recording medium in order to increase recording density among the performance characteristics of a recording head. To achieve this, it is required to implement a recording head of a narrow track structure wherein the width of top and bottom poles sandwiching the recording gap layer on a side of the air bearing surface is reduced down to microns or the order of submicron. Semiconductor process techniques are utilized to implement such a structure.
Reference is now made to FIG. 13A to FIG. 16A, FIG. 13B to FIG. 16B and FIG. 17 to describe an example of a method of manufacturing a composite thin-film magnetic head as an example of a related-art method of manufacturing a thin-film magnetic head. FIG. 13A to FIG. 16A are cross sections each orthogonal to an air bearing surface of the thin-film magnetic head. FIG. 13B to FIG. 16B are cross sections of a pole portion of the head each parallel to the air bearing surface.
In the manufacturing method, as shown in FIG. 13A and FIG. 13B, an insulating layer 102 made of alumina (Al2O3), for example, having a thickness of about 5 to 10 μm is deposited on a substrate 101 made of aluminum oxide and titanium carbide (Al2O3—TiC), for example. On the insulating layer 102 a bottom shield layer 103 made of a magnetic material is formed for making a reproducing head.
Next, on the bottom shield layer 103, alumina, for example, is deposited to a thickness of 100 to 200 nm through sputtering to form a bottom shield gap film 104 as an insulating layer. On the bottom shield gap film 104 an MR element 105 for reproduction having a thickness of tens of nanometers is formed. Next, a pair of electrode layers 106 are formed on the bottom shield gap film 104. The electrode layers 106 are electrically connected to the MR element 105.
Next, a top shield gap film 107 is formed as an insulating layer on the bottom shield gap film 104 and the MR element 105. The MR element 105 is embedded in the shield gap films 104 and 107.
Next, on the top shield gap film 107, a bottom pole layer 108 that also functions as a top shield layer, having a thickness of about 3 μm, is formed. The bottom pole layer 108 is made of a magnetic material and is used for both a reproducing head and a recording head.
Next, as shown in FIG. 14A and FIG. 14B, on the bottom pole layer 108, a recording gap layer 109 made of an insulating film such as an alumina film whose thickness is 0.2 μm is formed. Next, a portion of the recording gap layer 109 is etched to form a contact hole 109a to make a magnetic path. On the recording gap layer 109 in the pole portion, a top pole tip 110 made of a magnetic material and having a thickness of 0.5 to 1.0 μm is formed for the recording head. At the same time, a magnetic layer 119 made of a magnetic material is formed for making the magnetic path in the contact hole 109a for making the magnetic path.
Next, as shown in FIG. 15A and FIG. 15B, the recording gap layer 109 and the bottom pole layer 108 are etched through ion milling, using the top pole tip 110 as a mask. As shown in FIG. 15B, the structure is called a trim structure wherein the sidewalls of the top pole (the top pole tip 110), the recording gap layer 109, and a part of the bottom pole layer 108 are formed vertically in a self-aligned manner.
Next, an insulating layer 111 made of an alumina film, for example, and having a thickness of about 3 μm is formed on the entire surface. The insulating layer 111 is then polished to the surfaces of the top pole tip 110 and the magnetic layer 119 and flattened.
Next, on the flattened insulating layer 111, a first layer 112 of a thin-film coil is made of copper (Cu), for example, for the induction-type recording head. Next, a photoresist layer 113 is formed into a specific shape on the insulating layer 111 and the first layer 112. Heat treatment is then performed at a specific temperature to flatten the surface of the photoresist layer 113. On the photoresist layer 113, a second layer 114 of the thin-film coil is then formed. Next, a photoresist layer 115 is formed into a specific shape on the photoresist layer 113 and the second layer 114. Heat treatment is then performed at a specific temperature to flatten the surface of the photoresist layer 115.
Next, as shown in FIG. 16A and FIG. 16B, a top pole layer 116 is formed for the recording head on the top pole tip 110, the photoresist layers 113 and 115, and the magnetic layer 119. The top pole layer 116 is made of a magnetic material such as Permalloy. Next, an overcoat layer 117 of alumina, for example, is formed to cover the top pole layer 116. Finally, machine processing of the slider is performed to form the air bearing surface 118 of the thin-film magnetic head including the recording head and the reproducing head. The thin-film magnetic head is thus completed.
FIG. 17 is a top view of the thin-film magnetic head shown in FIG. 16A and FIG. 16B. The overcoat layer 117 and the other insulating layers and insulating films are omitted in FIG. 17.
In FIG. 16A, ‘TH’ indicates the throat height and ‘MR-H’ indicates the MR height. The throat height is the length (height) of portions of magnetic pole layers facing each other with a recording gap layer in between, between the air-bearing-surface-side end and the other end. The MR height is the length (height) between the air-bearing-surface-side end of the MR element and the other end. In FIG. 16B, ‘P2W’ indicates the pole width, that is, the recording track width. In addition to the throat height, the MR height and so on, the apex angle as indicated with θ in FIG. 16A is one of the factors that determine the performance of a thin-film magnetic head. The apex is a hill-like raised portion of the coil covered with the photoresist layers 113 and 115. The apex angle is the angle formed between the top surface of the insulating layer 111 and the straight line drawn through the edges of the pole-side lateral walls of the apex.
In order to improve the performance of the thin-film magnetic head, it is important to precisely form throat height TH, MR height MR-H, apex angle θ, and track width P2W as shown in FIG. 16A and FIG. 16B.
To achieve high surface recording density, that is, to fabricate a recording head with a narrow track structure, it has been particularly required that track width P2W fall within the submicron order of 1.0 μm or less. It is therefore required to process the top pole into the submicron order through semiconductor process techniques.
A problem is that it is difficult to form the top pole layer on the apex into small dimensions.
As disclosed in Published Unexamined Japanese Patent Application Hei 7-262519 (1995), for example, frame plating may be used as a method for fabricating the top pole layer. In this case, a thin electrode film made of Permalloy, for example, is formed by sputtering, for example, to fully cover the apex. Next, a photoresist is applied to the top of the electrode film and patterned through a photolithography process to form a frame to be used for plating. The top pole layer is then formed by plating through the use of the electrode film previously formed as a seed layer.
However, there is a difference in height between the apex and the other part, such as 7 to 10 μm or more. The photoresist whose thickness is 3 to 4 μm is applied to cover the apex. If the photoresist thickness is required to be at least 3 μm over the apex, a photoresist film having a thickness of 8 to 10 μm or more, for example, is formed below the apex since the fluid photoresist goes downward.
To implement a recording track width of the submicron order as described above, it is required to form a frame pattern having a width of the submicron order through the use of a photoresist film. Therefore, it is required to form a fine pattern of the submicron order on top of the apex through the use of a photoresist film having a thickness of 8 to 10 μm or more. However, it is extremely difficult to form a photoresist pattern having such a thickness into a reduced pattern width, due to restrictions in a manufacturing process.
Furthermore, rays of light used for exposure of photolithography are reflected off the base electrode film as the seed layer. The photoresist is exposed to the reflected rays as well and the photoresist pattern may be out of shape. It is therefore impossible to obtain a sharp and precise photoresist pattern.
As thus described, it is difficult in prior art to fabricate the top pole layer with accuracy if the pole width of the submicron order is required.
To overcome the problems thus described, a method has been taken, as shown in the foregoing related-art manufacturing steps illustrated in FIG. 14A to FIG. 16A and FIG. 14B to FIG. 16B. In this method, a track width of 1.0 μm or less is formed through the use of the top pole tip 110 effective for making a narrow track of the recording head. The top pole layer 116 to be a yoke portion connected to the top pole tip 110 is then fabricated (as disclosed in Published Unexamined Japanese Patent Application Sho 62-245509 [1987] and Published Unexamined Japanese Patent Application Sho 60-10409 [1985]). That is, the ordinary top pole layer is divided into the top pole tip 110 and the top pole layer 116 to be the yoke portion in this method. As a result, it is possible that the top pole tip 110 that defines the track width is formed into small dimensions to some degree on the flat top surface of the recording gap layer 109.
However, the following problems are still found in the thin-film magnetic head having a structure as shown in FIG. 16A and FIG. 16B.
In the thin-film magnetic head shown in FIG. 16A and FIG. 16B, the recording track width is defined by the top pole tip 110. Therefore, it is not necessary that the top pole layer 116 is processed into dimensions as small as those of the top pole tip 110. However, if the recording track width is extremely reduced, that is, down to 0.5 μm or less, in particular, processing accuracy for achieving the submicron-order width is required for the top pole layer 116, too. However, the top pole layer 116 is formed on top of the apex in the head shown in FIG. 16A and FIG. 16B. Therefore, it is difficult to reduce the top pole layer 116 in size, due to the reason described above. In addition, the top pole layer 116 is required to be greater than the top pole tip 110 in width since the top pole layer 116 is required to be magnetically connected to the top pole tip 110 smaller in width. Because of these reasons, the top pole layer 116 is greater than the top pole tip 110 in width in this thin-film magnetic head. In addition, the end face of the top pole layer 116 is exposed from the air bearing surface. As a result, writing may be performed by the thin-film magnetic head on a side of the top pole layer 116, too, and so-called ‘side write’ may result, that is, data is written in a region of a recording medium where data is not supposed to be written. Such a problem more frequently results when the coil is two-layer or three-layer to improve the performance of the recording head and the apex is thereby increased in height, compared to the case where the coil is one-layer.
Furthermore, it is difficult to reduce the magnetic path (yoke) length of a prior-art magnetic head. That is, if the coil pitch is reduced, a head with a reduced yoke length is achieved and a recording head having an excellent high frequency characteristic is achieved, in particular. However, if the coil pitch is reduced to the limit, the distance between the zero throat height position (the position of the air-bearing-surface-side end of the insulating layer that defines the throat height) and the outermost end of the coil is a major factor that prevents a reduction in yoke length. Since the yoke length of a two-layer coil can be shorter than that of a single-layer coil, a two-layer coil is adopted to many of recording heads for high frequency application. However, in the prior-art magnetic head, a photoresist film having a thickness of about 2 μm is formed to provide an insulating film between coil layers after a first layer is formed. Consequently, a small and rounded apex is formed at the outermost end of the first layer of the coil. A second layer of the coil is then formed on the apex. The second layer is required to be formed on a flat portion since it is impossible to etch the seed layer of the coil in the sloped portion of the apex, and the coil is thereby shorted.
Therefore, if the total coil thickness is 2 to 3 μm, the thickness of the insulating film between the layers of the coil is 2 μm, and the apex angle is 45 to 55 degrees, for example, the yoke length is required to be 6 to 8 μm which is twice as long as the distance between the outermost end of the coil and the neighborhood of the zero throat height position, that is, 3 to 4 μm (the distance between the innermost end of the coil and the portion where the top and bottom pole layers are in contact with each other is required to be 3 to 4 μm, too), in addition to the length of the portion corresponding to the coil. This length of the portion other than the portion corresponding to the coil is one of the factors that prevent a reduction in yoke length.
Assuming that a two-layer eleven-turn coil in which the line width is 1.2 μm and the space is 0.8 μm is fabricated, for example, the portion of the yoke length corresponding to the first layer 112 of the coil is 11.2 μm, if the first layer is made up of six turns and the second layer is made up of 5 turns, as shown in FIG. 16A and FIG. 16B. In addition to this length, the total of 6 to 8 μm, that is, the distance between each of the outermost and innermost ends of the first layer 112 of the coil and each of ends of the photoresist layer 113 for insulating the first layer 112, is required for the yoke length. Therefore, the yoke length is 17.2 to 19.2 μm. If an 11-turn coil is made up of one layer, the yoke length is 27.2 to 29.2 μm. In the present patent application, the yoke length is the length of a portion of the pole layer except the pole portion and the contact portions, as indicated with L0 in FIG. 16A. As thus described, it is difficult in the prior art to further reduce the yoke length, which prevents improvements in high frequency characteristic.
In order to connect the first layer of the coil to the second layer of a prior-art head, a contact hole is made in an insulating layer covering the first-layer of the coil, the contact hole being provided in a region where the first layer is connected to the second layer. This is similar to the case where the coil is connected to a lead, that is, a contact hole is made in the insulating layer covering the coil in a region where the coil is connected to the lead. Therefore, additional steps are required for making the contact holes when the thin-film magnetic head is manufactured. Moreover, additional photomasks are required for making the contact holes.